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$Id: BuildingLCX.html 396 2014-02-11 16:29:59Z mrwhat $

Building laser cut Sleipnir Walin8r
Streamlined Xerocraft Configuration

This build is quicker and a bit more lightweight than previous builds, using less hardware, but requires the ability to cement acrylic.
These drawings will help explain my conventions for naming parts of the linkage:

Less-common tools needed (beyond screwdriver, small wrench, file, sandpaper...):

Expendible materials:

23/16" OD hard steel rod, 12" in length
#10-32 nyloc nuts
#10-32 nuts
#10 lockwashers
81/2" long, 3/16" OD #4-40 round female-female standoffs
21/2" long, #4-40 threaded rods.
May be constructed by cutting the head off of a #4-40 screw, and cleaning the threads.
4#4-40 flat-head screws, 3/8" long
6#4ish self-piloting plastic screws, 1/4" long
32#4-40 screws, 1/2" long. 4 spindles
3*8 hinges
4 motor driver mount
12#4-40 screws, 7/8" long. 4 motor mounts
8 hinges
4#4-40 screws, 1 1/8" long. (main bar)
4#4-40 screws, 1/4" long. (spindles)
8#4-40 nuts
Can use these while cementing parts
Main bar and motor mounts
36#4-40 nyloc nuts 4*8 hinges
4 motor driver mount
16#4 internal tooth lockwashers 4 motor mounts
4 main bar
8 spindles (both sides)
14larger diameter #4 washers 2 motor gears
4*2 on spindles
4 under crank-arm
90#4 washers 2*4*8 hinges
4 on spindles
8 motor mount
8 main bar
6 lid tabs
121/4" long, 3/16" ID nylon spacers on B-axle
to space out legs
81/2" long, 3/16" OD #4 nylon spacers hinges
363/16" long, 3/16" OD #4 nylon spacers 3*8 hinges
8 hip-B fillers
4 motor driver mount
723/16" ID nylon washers (#10), around 1mm thick ~3*8 spindles
~16 B-axle
2*2*8 hinges

Main assembly parts:

For Uno-based Bluetooth remote control electronics:

General note on glues for Acrylic:
Do NOT use CA cement on or near acrylic. The fumes will mar and glaze the surface. Welding agents work wonderfully when bonding acrylic to acrylic. I am told that acetone will work, but it is slow, and may not make as strong a weld as the Weld-On chemicals. The weld strength is not likely to be an issue for this assembly, which does not experience any severe stresses. I have been using Weld-On #3 which is very fast. I am told that Weld-On #4 will be a bit slower and make a stronger weld. I am finding #3 too fast, and rather hard to work with, so I will recommend getting #4 if you can.

Welding is unnecessary for most of this project, simply an asthetic decision. However, welding the main drive gear to it's guidance plates should make the gear teeth a little stronger, which might be a good idea.

It may not be necessary to epoxy the motor gear to the shaft, but it should certainly make that connection stronger, and perhaps longer-lived.

Chassis assembly

Chassis assembly is into several major stages. The first stages involve the use of epoxy which may take a significant amount of time to set. This stage can be performed in parallel with the next two stages while waiting for adhesives to cure.

These are still being re-written from the previous build configuration. This text should be augmented with illustrated, detailed step instruction pages as they become available

  1. Cement main axle and gear
    Roughen gear near axle hole, and ends of axle standoffs.
    Center threaded rod on gear, dab a little cement, install standoffs to form an axle.
    clean excess epoxy, if any.
    set aside to cure
  2. Cement motor gear to motor axle
    Roughen one side of a wider washer, and slip over motor axle, rough side out.
    Roughen one side of motor gear near axle hole, and one side of a motor gear hub piece.
    Place the gear, then hub on motor axle, with smooth sides facing each other
    Cement gear to hub while installed on axle.
    Drive the motor to make sure that gear is mounted perpendicular, and does not wobble as it turns.
    Allow cement to cure for a few minutes.
    Put some epoxy on top of the washer and at the edge of the gear hub
    Adhere the washer to the gear with epoxy, and the tip of the bub to the axle with epoxy.
    Drive the motor and check alignment
    allow to cure
  3. Counter-sink one side of one hole on crankarms
    Counter sink should not quite make head of screw flush with the crank. The screw head can and should stick out a little (deeper may make the crank arm too weak). The counter sink only needs to be deep enough to increase the contact area with the flat screw head a bit larger to adhere to epoxy later. The head only needs to be recessed a little bit in order to clear the crank-links on the spindle.
    Roughen the walls of the countersink a bit, and roughen the underside of the screw head with a file. They will be epoxied to the axle later in the assembly process.
  4. (Cut and) thread ends of axle rods
    If you do not want the axle tips to extend beyond the leg braces, you may wish to cut the axle rods. I do not (yet) know the exact desired length of the axle rods, so if you wish to cut them, you may want to assemble the robot with only one side threaded, measure the length, then remove, cut, and thread the other end when the desired lengths are known. I usually replace the axle with a shish-kabob skewer while working on the axle. this makes removing and replaceing the axle very easy.
    I have been putting a #10-32 thread about 0.5-0.8" long on each end of the axle.
  5. Bevel main gear side plates (optional)
    A bevel on the inside of the drive gear side plates may help keep the larger diameter motor gear centered on the drive gear.
    To bevel these gears, I screw them onto a standoff, then put them in an electric drill. I then take the electric drill to a sander and simultaneously turn the plate with the drill and touch it to the sander to make an even circular bevel.
    The bevel should not quite go the full thickness of the plate, and be at an angle not more than about 60 degrees, making the thickness of the bevel no more than about 3mm (0.15")
  6. Cement main gear side plates to main gear (optional)
    The teeth of the main gear might be strengthened by cementing them to the side plates. If you wish to do this, slide the side-plates on the axle, bevel side in (if beveled), and cement them in place.
  7. Cement forks to Hip and Foot pieces
    Place about 5mm worth of stackers on the hip or foot piece under one of the wider fork pieces. If your 4.5mm stock is near 4.5mm, it will be sufficient. If this stock runs a little thin, try stacking one 2.2(2.5)mm stacker with one 3mm stacker. Align the fork and stackers with a 7/8" to 1" screw and nut, loosely. Apply the solvent to the edges so that it will capilary between the pieces, then snug (do NOT tighten) the screws until the cement adheres.
    Do NOT tighten, it will not strengthen the bond, and may crack the acrylic.
    Allow the cement to cure.

    Note that there will be 4 left-handed, and 4 right-handed hip and foot pieces.
    When the forks are installed "on top" of the foot/hip piece, half should face one direction, and the other half should face the other direction.

    After the wide forks have been installed, install the narrow hip forks in a similar fashion. The hip-D attachment will have two forks tynes, instead of one fork tyne on top of stackers. If your 4.5mm stock is actually thinner than 4.4mm, you may want to cement a thin PETG shim under one of the fork tynes. I recommend installing the shim UNDER each left-hand hip, and ON TOP of each right-hand hip. (Which one is "left" and "right" is not critical, just that you maintain symetry)

  8. Assemble legs
    This one really needs its own page. The Leg sub-assemblies process is the similar to the one for the bolted assemblies just ignore the bolts on the forks in the photos. Cementing these forks is stronger, lighter, cheaper, faster, and more reliable.

    We are now using a screw with a nylon spacer, 2 flat washers, and a nylock for each hinge instead of a standoff, two screws, two flat washers and two lock washers.
    I am no longer recommending the additional braces on EF or BH. (Unnecessary weight and complexity)

    Nylon spacer hinges should have snug, but not tight nyloc nuts. I usually tighten them until I feel some resistance, then back off 1/4 turn.

  9. Assemble main bar with drivetrain
    Cement the crescent from under the motor mount to the crescent shaped motor brace with screw-holes.
    Install a flat washer under the head of a 7/8" screw, and place this screw through one side of the motor fork.
    Then install the cemented crescent brace onto this screw, followed by two spacers, then the oval-shaped motor brace piece. Secure with a washer, lock-washer, and nut, loosely.

    Install 3 braces on each side of the main bar with 1 1/8" screws with a flat washer below the head.
    Then install the main gear axle onto the motor-mount side of the main bar, on the same side as these braces (opposite side of motor clip).
    Install the other side of the main bar onto these screws, and secure loosely with a washer, lockwasher, and nut.

    Slide the motor and gear assembly into place from the bottom.
    Place the crescent motor brace and back clip around the motor holding it into place.
    Rotate the motor gear until the hole is over the un-secured side of the motor fork. Install the other screw and washer by passing them through this hole. Plase 2 more spacers behind the crescent motor brace, then secure the back side of the motor clip onto the screw with a washer, lockwasher, and nut.
    A screwdriver may be used to brace this screw as the nut is tightened.
    Move the hole to lay over the other screw, brace it, and tighten the other nut.

    Make sure the brace holes are alighed to cover the axle hole, and tighten these screws.

  10. Epoxy crank arm to drive gear axle
    Place an internal tooth lock-washer and then a flat washer on a 1/2" screw. Insert this screw through the non-countersunk hole, with the head on the opposite side as the countersink.
    Put a wide flat-washer on the other side of this screw, secured with a round standoff. Tighten the screw enough to engage the lock-washer securing the standoff in place.
    You may want to locktite this screw, since it can be hard to get to after the crankarms have been cemented in place.

    Roughen the crank-arm inside the counter sink, and near the hole on the other side. Apply some epoxy (JB-Weld) and screw this crank-arm to the main gear axle snugly.

    Repeat for the other side, making sure that the crank arms are exactly opposing each other (180 degrees apart), and allow to set.

  11. Integrate payload bay
  12. Mount cranklinks onto spindles
  13. Mount main drive and leg assemblies to axles
  14. Complete axle assemblies with brace
  15. test
  16. Install payload lid

Save the following LINKS to get production drawings:
The production drawings will not render in your browser. The lines are too thin.
Naming convention
XDXerocraft layout, linkage configuration D
20scaled for 20mm crank arms
Layout for 2.2, 3.0, 4.5mm acrylic respectively
XXXxYYYScale of rectangle containing drawing, in mm
I think that ponoko's "2mm" acrylic is actually some manufacturer's 0.100", which runs a little thin, close to 2.2mm, which is about 1/2 the thickness of the 4.5mm stock, as needed. It appears that the 0.098" stock at Creative plastics in Tuscon also runs about 2.2mm thick.

This scale in the filename is for a rectangle containing the outside tips of the corner fiducials. This should make it easier to import the drawings, just set the scale of the imported object to the size referenced in the file name.
The spacing from center to center of the fiducials is actually 1mm less than the numbers in the file name.

Here are the (depricated) instructions for building using standoffs. They may be helpful, but they are to be replaced by the above procedure.
  1. Drive and main bar assembly
  2. Leg sub-assemblies
  3. Payload assembly
  4. Main chassis integration

Last modified: 131007

Aaron Birenboim